View Full Version : Cyanotype Rex

01-17-2006, 12:37 PM
I've been trying to read up on the recently "retro-invented" process called Cyanotype Rex. It came about by way of trying to recreate William Herschel's original work that created the cyanotype, wondering why he went about it the way he did instead of just mixing the chemicals together as is done today -- but the end result has been the discovery that perhaps Herschel was a little smarter than the last 160 years gives him credit for.

Cyanotype is created by mixing ferric ammonium citrate and potassium ferricyanide solutions, and coating paper (or fabric) with the result. Once dry, the paper is exposed to strong blue/UV light until the image prints out, then begins to reverse (the blue exposed material starts to turn silvery gray); once the print is judged to be sufficiently overprinted, it is "developed" by washing in plain or slightly acidified water to remove the unreacted sensitizer and leave the blue image (which darkens with exposure to air). This "blueprint" process has been in use for various applications, including duplicating engineering drawings, for more than 150 years.

However, this isn't the way Herschel did it.

According to researchers, the original method was to coat the paper with only the ferric ammonium citrate (or ferric oxalate), expose briefly to produce a very faint printed-out image, then develop with the second chemical, which can be the same potassium ferricyanide for a classic blue, negative-image Cyanotype Rex, or potassium ferrOcyanide to produce a direct positive, or a gold bearing solution to produce an image in metallic gold (ranging from nearly black, to pink, blue, or even metallic appearing) called Chrysotype Rex, or with silver to produce the classic kallitype.

Unfortunately, the details are sketchy -- a Google search turned up a page by the "retro-inventor" of the process, but he didn't give exact details (mixing formulae etc.) for any of the processes; I had to read between the lines even to determine that the basic Cyanotype Rex uses the same chemicals as the "traditional" cyanotype. I expect those who rediscovered this form of cyanotype are trying to preserve their ability to collect money for workshops, at least for a while. What especially struck me, however, was one of the images on that page -- an 8x10 in-camera Cyanotype Rex negative, from which (the caption claims) they have subsequently made a positive print (yes, a cyanotype print from a paper negative). Exposure times with a lens apparently run to a few seconds in bright sun, making this process comparable in speed to Daguerreotype and collodion wet plate; they also claim UV isn't necessary, which with the relatively high speed opens the possibility of enlarging onto Cyanotype Rex. In addition, they've done coatings on fixed-out silver gelatin paper, which gives a very smooth surface capable of recording fine detail, unlike the rough watercolor finishes more commonly used for cyanotypes (especially by those who can't afford to spend $100 for a packet of high-end alt-process paper).

Of course, using the same chemicals in similar quantity means Cyanotype Rex prints can be made for pennies per sheet, not counting the paper cost; if you buy the two basic chemicals in bulk and have access to a suitable sized paper at reasonable cost, it might well cost less than even discount enlarging paper.

Apropos to our interests -- if you can expose in a few seconds at, say, f/11 or f/16, you can expose in under an hour at f/256; that is, this process is comparable in speed to the slower end of the enlarging papers pinhole photographers sometimes use for negatives (which isn't bad for a process originally invented in the 1830s).

Tom Persinger
01-17-2006, 12:47 PM
IM- you can read several posts about this in the alt-process email group archives:

Terry King (the retro-inventor you refer to in your post) will be present at the f295 Symposium, I'm sure he would welcome your questions & comments at the DIY/Alt-process session.

All others interested:
You can read his article from View Camera magazine online:
Chrysotype Rex and Cyanotype Rex: A Revolution in Iron Based Processes

and, you can see his website here:

I'm not in a position to evaluate his research or comment on Herschel's process ;)

Tom Persinger
01-26-2006, 08:48 AM
IM et al-
Gustavo Castilla has posted some info re: the Cyanotype Rex formula over at APUG, I repeat it here...

Rex Cyanotype anc Chrysotype
Coate paper with Ferric Oxalate (add a bout 5 gr of wood bleach aka Oxalil acid to solution) it takes about 1 .5 ml for an 8x 10 expose and develop on Potassium ferricyanide ( about 30 grms fo 1 Lt of water MAKE sure to use destild water) for the gold print use same solution to coate paper and develop on 8% gold chloride solution carfull about $30.00 for an 8X10 the developer is a one time shot how ever the used solution can be used as gold toner do not try to develop more then one print at a time start small 6x7 is fine put gold solution on a small bottle so that you can pour only as much as to get paper wet all over
is a relative fast developer akin to PL PT

the link:

01-30-2006, 06:08 PM
Cool! I haven't been back to APUG since my hard disk failure Thursday evening -- I'll pick up the thread over there. And then, I'll try some Rex prints under my enlarger; looks to me (from other readings) that I can use my existing ferric ammonium citrate solution as sensitizer, get faster print but not as much "quality", and I can dilute my existing potassium ferricyanide solution for the developer (have to look up how much ferri is in the water, but that's easy enough).

Looking forward to the possibility of making Rex prints directly from 35 mm negatives, even if I *do* have to work under safelight... ;)

03-14-2006, 09:05 PM
my 2 cents
I was expecting to get a Chrysotype on the paper quoted here (viewcamera) But Terry lost the print .
the procces is rather simple and any paper will work from cot320 to marker paper
I find that is important to me any how to find a paper the will help the Image as the emultion and paper become one ( hard to see on computer screen) so I will recomend not to shy away from the process Cyanotype is rather afortable .
100of potassium ferricyanide 10.00
Amonium Ferric Oxalet another 10 .00 for 100 grms and boy with this 20.00 buck you can print until you get blue on the face at list 200 prints for 20.00 plus paper